The deposition of extracellular amyloid fibrils in cores of senile plaques and walls of blood vessels is a hallmark of aging, Alzheimer's disease (AD), and Down's syndrome. Recent identification of the amyloid precursor protein (APP) gene and resultant transcripts provides the opportunity to examine the molecular biology of this gene and gene products as well as cellular mechanisms that may lead to amyloid deposition. Localization of this gene on chromosome 21, together with the identification of a disease locus in familial AD (FAD) to the same chromosome, would provide impetus for the concept that abnormalities of molecular regulation may underlie the pathogenesis of AD. Therefore, the goals of Project 1 are designed to study the expression of the APP transcripts and to facilitate localization of the FAD gene by obtaining a more precise map of chromosome 21. Because differential expression of alternatively spliced APP mRNA may be one mechanism that contributes to amyloidogenesis, two of our studies are designed to analyze levels of expression of the mRNA in different brain regions and in different cell types. We will use RNA in different brain regions and in different cell types. We will use RNA blotting and in situ hybridization t o correlate levels of expression of APP mRNA with the deposition of amyloid. Moreover, we will investigate the biology of encoded proteins by the introduction of APP gene constructs into mammalian cells. Because proteins encoded by various APP mRNA may have different biological functions and activities, transfection studies provide a convenient vehicle to test these parameters. Our proposed studies should provide insights into the localization, function, and posttranslational processing of the proteins. In concert, these studies will provide much information concerning the biology of the APP gene and its products. In addition, we may identify differential expression of APP mRNA and alterations in protein processing that may contribute to amyloid deposition. Finally, we will delineate more precise markers of chromosome 21 in the region of the putative FAD locus. Ongoing efforts to locate the FAD gene require the availability of more chromosome 21 markers. Therefore, we propose to obtain and identify markers of chromosome 21 by constructing a linkage map of this chromosome and to test for linkage of these markers in families with AD.